1. Field of the Invention
The present invention relates to a photosensitive resin composition for a flexographic printing plate.
2. Description of the Related Art
In the field of printing, the importance of a flexographic printing method has become greater and greater because of the diversification of substances to be printed as well the consumer's taste. Further, the importance of a water developable type flexographic printing plate system has recently become greater from the view point of environmental pollution, working conditions and the like.
Heretofore, various photosensitive compositions which provide a water developable flexographic printing plate have been suggested. In a conventional technique, it is required that the constituent resin component have the following characteristic, (1) solubility to water or alkali water, and (2) dispersibility or lubricity to the developer, so as to impart water developability to the composition. A particularly preferred form of the resin is a main binder resin having elasticity in the form of an elastic particle containing a conjugated diene compound as a main component.
Japanese Patent Kokai No. 63-1962712 discloses a conjugated diene copolymer and a photosensitive resin composition obtained by using the same. This conjugated diene copolymer has the particulate form, wherein a three-dimensionally crosslinked structure is continuously distributed from the inside to the outside of the particle. In the case of this particle, it is difficult to design the surface and the three-dimensionally crosslinked structure. Further, storage stability of the resulting flexographic printing plate is inferior and water developability is insufficient.
Furthermore, Japanese Patent Kokai No. 2-175702 discloses a photosensitive composition containing a core/shell type microgel, which can be treated with water. The microgel used is a microgel having a core/shell structure of two layers, wherein only the core portion in the particle has a three-dimensionally crosslinked structure. However, this resin particle has a water swelling property and water resistance of the resulting plate which is inferior. Further, viscosity of the photosensitive composition becomes high on production and strong entanglement of the resin occurs on kneading. Water developability and storage stability of the resulting printing plate are also inferior.
The main object of the present invention is to provide a photosensitive composition which provides a water developable flexographic printing plate. That is, by using a microgel resin having a specific structure, there is provided a photosensitive composition having excellent water developability and storage stability, wherein surface design of the particle is easily conducted and the particle per se has excellent water resistance, whereby, kneading is easily conducted on the production of the plate and solid retention of the plate is superior.
These objects as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.